This invention relates in general to electrostatic discharge (ESD) protection circuits, and in particular to an electrostatic discharge protection circuit placed between an oscillator input pin and an oscillator output pin to protect a feedback element located between these pins.
In metal-oxide-silicon (MOS) chips, electrostatic discharges caused by human handling of the chips can permanently damage the metal-oxide-silicon field effect transistors (MOSFETs) on the chips. For example, the thin oxide layer that isolates the gate from the substrates in a MOSFET can be ruptured by the ESD voltage surge. Additionally, the metal layer attached to the drain or source diffusion region can spike through this diffusion region to the substrate below. Prior art ESD protection circuitry protects the MOSFETs from ESD voltage surges between a pin and the power and protects the MOSFETs against ESD voltage surges between a pin and the ground.